Patent AU-2017100579-A4 (AU)
Title: Pulse induction metal detector using a convolution error feedback amplifier
Inventor: MOODY PAUL GERARD
IPC: G01V3/10
Filed: 2017-05-21
Granted: 2017-06-22
Abstract: PATENTS ACT 1990 COMPLETE SPECIFICATION FOR AN INNOVATION PATENT Name of Applicant: Paul Gerard Moody Actual Inventor: Paul Gerard Moody Address for Service: 55 Hunter Street, Brunswick West, 3055, Victoria, Australia Invention Title: PULSE INDUCTION METAL DETECTOR USING A CONVOLUTION ERROR FEEDBACK AMPLIFIER The following statement is a full description of this invention, including the best method of performing it known to me. The whole of provisional patent application, titled : "PULSE INDUCTION METAL DETECTOR USING A CONVOLUTION ERROR FEEDBACK AMPLIFIER", Australian application number: 2016902385 is wholly incorporated by reference in respect of the present invention priority date, description, drawings and claims set out herein. PULSE INDUCTION METAL DETECTOR USING A CONVOLUTION ERROR FEEDBACK AMPLIFIER A pulse induction metal detector having at least three sequential states, each state 5 being a non zero period of time, a first state where a magnetic pulse, due to the flow of electric current controlled by a first switch, is emitted from a first coil, a second state where a back EMF being a high voltage is present across the first coil for a period of time due to abrupt cessation of electrical current flowing in the first coil, a third state being a receive state where residual current from the first and .0 second states and induced currents from conductive targets, mains frequency, earth magnetic field and ground in vicinity of the first coil result in a signal voltage across the first coil, includes the aforementioned coil for pulsed emission and detection of a time varying magnetic field, a means for damping a back EMF across the aforementioned coil, a first diode conducts during the aforementioned second .5 period protecting input electronics from the high voltage back EMF that may exist across the first coil, a first amplifier configured as an integrator performing an integration of the voltage across the coil during each receive period, a second switch connecting the output of the first amplifier during at least one receive period to the input of a second amplifier configured as an integrator, the second switch and .0 second amplifier thus demodulating and reconstructing a time varying voltage waveform, representative of the unwanted convolution error signal voltage, at the output of the second amplifier which is connected to a summation point at the input to the first amplifier forming a negative feedback loop, the loop gain having a negative sign, where the sample timing of the second switch and the time constant .5 of the second integration amplifier are adjusted by a suitable control means as known in the art such that unwanted convolution spectral components are demodulated and fed back into a summing point at the input of the first amplifier and thus the magnitude of unwanted signals in the output of the first amplifier is reduced. Page 2 of 15 PULSE INDUCTION METAL DETECTOR USING A CONVOLUTION ERROR FEEDBACK AMPLIFIER CD + Iwt C41± Page 13 of 15